Question

有人知道如何在实体中使用JPA 2.1创建Set String类型吗？我希望它作为目录工作，因此不存在重复的值（如枚举）。

我试过了：

 @ElementCollection(fetch = FetchType.EAGER, targetClass = String.class)
  @CollectionTable(
      name = "transactions_labels",
      joinColumns = @JoinColumn(name = "id"),
      foreignKey = @ForeignKey(name = "transaction_id"),
      uniqueConstraints = @UniqueConstraint(columnNames = "label", name = "unique_label")
  )
  @Column(name = "label")
  public Set<String> labels;

不幸的是，这会在transactions_labels表格中创建重复项，其中多个条目在transactions_labels.label中包含相同的值。

我希望JPA在插入新值之前检查该值是否存在。

这可能吗？

JPA坚持：

TransactionEntity transactionEntity = new TransactionEntity();
entityManager.persist(transactionEntity);
[...]
transactionEntity.labels = new HashSet<>();
transactionEntity.labels.add("some_tag_1");
transactionEntity.labels.add("some_tag_2");
transactionEntity.labels.add("some_tag_3");
[...]
entityManager.getTransaction().commit();

Hibernate生成的SQL（删除了一些字段）：

Hibernate: 
    insert 
    into
        transactions
        ([...]) 
    values
        (?, ?, ?, ?, ?, ?, ?, ?)
Hibernate: 
    update
        transactions 
    set
        [...]
    where
        id=?
Hibernate: 
    insert 
    into
        transactions_labels
        (id, label) 
    values
        (?, ?)
Hibernate: 
    insert 
    into
        transactions_labels
        (id, label) 
    values
        (?, ?)
Hibernate: 
    insert 
    into
        transactions_labels
        (id, label) 
    values
        (?, ?)

字符串的JPA 2.1 ElementCollection或OneToMany

0 个答案: